Ultrasound hair drying and styling

ABSTRACT

An ultrasound hair care device (10) for drying and styling hair (20). An ultrasound unit (12-18) applies ultrasound to the hair (20). A hair moisture measurement unit (22) measures a moisture level of the hair (20). A control unit (24) controls the ultrasound unit (12-18) based on the moisture level. In accordance with the present invention, in dependence on the moisture level, ultrasound is applied to the hair (20) at a first frequency not exceeding 1 MHz for drying the hair (20), and/or at a second frequency of at least 1 MHz for styling the hair (20).

FIELD OF THE INVENTION

The invention relates to an ultrasound hair care device and method for drying and styling hair.

BACKGROUND OF THE INVENTION

Many women are concerned about hair damage resulting from styling and are sometimes dissatisfied with the results obtained from present styling devices. In general, there is awareness that applying heat to the hair will cause damage. The term hair styling as used herein is intended to encompass all actions such as hair crimping, curling, perming and straightening.

Traditional electrical hair styling devices use hot irons designed to give a thermal treatment to the hair fibers or lock of fibers while pressing them into a desired shape. The combination of excessive heating and/or weathering with mechanical (shear) forces during styling and combing leads to moisture loss and potential hair damage. Another problem is styling when hair is still damp or wet. This can create additional damage to the hair structure or might decrease the efficacy of the treatment.

US 2012/0291797 discloses a hair styling apparatus that includes a hair-heating device for applying heat to hair. The hair-heating device has a moisture-temperature setting and a dry-temperature setting less than moisture-temperature setting. A moisture sensor detects a moisture-indicating parameter of the hair, and generates a moisture-indicating signal indicative of whether the hair is at or below a predetem 1 ined moisture threshold level. A control circuit adjusts the temperature of the hair-heating device from the moisture-temperature setting to the dry-temperature setting in response to the moisture sensor generating a moisture indicating signal indicative of the hair being at or below the predetermined moisture threshold level. The hair-heating device is active in the dry-temperature setting.

US 2012/0312320 mentions that some hair styling tools incorporate the distribution of steam, ultrasonic waves, or active hair treatment compositions in addition to the application of heat, and that there are various methods for measuring moisture content in hair via observing electrical conductance, impedance, resistance, ultrasound, etc. No details are mentioned.

US 2006/0272669 discloses hair styling appliances that utilize ultrasonic vibration for hair styling, and mentions that it is possible to atomize moisture inside hair to evaporate the moisture by ultrasonic vibration, even under room temperature. It is thus not necessary to use an extremely high temperature (e.g., 130° C.) in order to evaporate moisture inside hair, which high temperature causes denaturation of protein and scald.

SUMMARY OF THE INVENTION

It is, inter alia, an object of the invention to provide a practical ultrasound hair care device and method for drying and styling hair. The invention is defined by the independent claims. Advantageous embodiments are defined in the dependent claims.

The present invention is based on the new insight that nebulizing (the water for drying the hair) and styling with optimized but distinctively different ultrasound frequencies have significant benefits over using a single frequency range for both styling and drying with ultrasound. Moreover, styling can only be done in an optimal way when the hairs are dry. Drying the hairs before styling makes the styling to be performed at higher temperature which results in better retention of style and quicker styling so hairs will be exposed to high temperature for shorter periods of time. Both conventional and surface acoustic wave based ultrasound nebulization elements can be implemented in the haircare device.

A first aspect of the invention provides an ultrasound hair care device for drying and styling hair. An ultrasound unit applies ultrasound to the hair. A hair moisture measurement unit measures a moisture level of the hair. A control unit controls the ultrasound unit based on the moisture level. In accordance with the present invention, ultrasound is applied to the hair at a first frequency not exceeding 1 MHz for drying the hair, and/or at a second frequency of at least 1 MHz for styling the hair in dependence on the moisture level.

Advantageously, the first frequency does not exceed 0.5 MHz, and preferably does not exceed 0.4 MHz. The second frequency is advantageously at least 5 MHz, and preferably between 6.4 MHz and 500 MHz.

An ultrasound intensity is advantageously at least 1 W/cm², and preferably does not exceed 10 W/cm².

The control unit may comprise a look-up-table for switching the ultrasound unit to operate at the first frequency and/or at the second frequency in dependence on the moisture level.

A second aspect of the invention provides a hair care method of drying and styling hair, the hair care method comprising measuring a hair moisture level; and applying ultrasound to the hair at a first frequency not exceeding 1 MHz for drying the hair and/or at a second frequency of at least 1 MHz for styling the hair in dependence of the hair moisture level.

Advantageously, ultrasound is applied during a period not exceeding 2 minutes, and preferably not exceeding 1 minute.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first embodiment of an ultrasound hair care device for drying and styling hair in accordance with the present invention.

FIG. 2 schematically represents how the ultrasound frequencies for drying and styling can be applied over time.

FIG. 3 illustrates ultrasound threshold intensities of the three identified main mechanisms involved in hair drying and styling as a function of ultrasound intensity.

FIG. 4 shows a second embodiment of an ultrasound hair care device for drying and styling hair in accordance with the present invention.

DESCRIPTION OF EMBODIMENTS

FIG. 1 shows an embodiment of an ultrasound hair care device 10 for drying hair and styling of hair. A first ultrasound generator 12 generates ultrasound at a frequency between 20 kHz to 0.4 MHz. A second ultrasound generator 14 generates ultrasound at a frequency between 6.4 MHz to 500 MHz. A first ultrasound transducer 16 in electrical communication with the first ultrasound generator 12 applies ultrasound to the water in hair lock 20 for nebulizing the water in hair lock as to dry hair. A second ultrasound transducer 18 in electrical communication with the second ultrasound generator 14 applies ultrasound to the hair lock 20 to style the hair. A hair moisture measurement unit 22 measures the moisture level of the hair lock 20. A control unit 24 controls a level of energy of the first ultrasound generator 12 and the second ultrasound generator 14 based on the measured hair moisture level as to provide optimum drying and styling to the hair.

Nebulization by means of ultrasound can be achieved within a frequency range of 20 kHz-1 MHz. To prevent cavitation, a frequency range of 20 kHz-0.4 MHz is preferably selected. Styling by means of ultrasound can be achieved within a frequency range of 1 MHz-500 MHz. To prevent cavitation, a frequency range of 6.4 MHz-500 MHz could be selected. Finally, moisture sensing by means of ultrasound can be achieved within a frequency range of 100 kHz to 1 MHz. The preferred range of intensity of an effective ultrasound-based hair styling device is between 1 W/cm² and 10 W/cm² measured at the transducer-hair interface.

FIG. 2 schematically represents how the ultrasound frequencies for drying D and styling S can be applied over time. Starting with wet hair, initially relatively much ultrasound energy is applied at the ultrasound frequency for drying D, and relatively little ultrasound energy is applied at the ultrasound frequency for styling S. However, over time, when the hair becomes gradually drier, the amount of ultrasound energy applied at the ultrasound frequency for drying D becomes smaller, and the amount of ultrasound energy applied at the ultrasound frequency for styling S becomes larger.

Three mechanisms of ultrasound styling have been proposed:

Heating; the hydrogen bonds are broken by increasing the temperature of the hairs above the glass transition temperature of hair.

Cavitation+heat; cavitation can decrease the power needed for styling with heat only

Non-thermal (i.e. mechanical vibrations); experiments have shown ultrasound as a means to break hydrogen bonds without using heat. Not using heat is a big advantage in order to avoid overheating during styling.

As shown in FIG. 2, ultrasound styling and drying can be accomplished with different as well as overlapping frequency ranges. An average power limit of 10 W/cm² and application time was set to max 60 s to maintain practical relevance.

FIG. 3 illustrates ultrasound threshold intensities of the three identified main mechanisms involved in hair drying and styling as a function of ultrasound intensity. The horizontal axis indicates frequencies in MHz, and the vertical axis indicates the threshold intensity in W/cm².

Curve A shows the threshold for styling through ultrasound heating (assuming all power is absorbed by hairs, 60 s).

Curve B shows the threshold for styling through ultrasound heating (60% relative humidity, matched to experiments, 60 s).

Curve C shows the threshold for nebulization (typical water film thickness), and curves C1-C2 show thresholds for nebulization (limits for 2-10 μm water film thickness).

Curve D shows the threshold for cavitation.

Region 1 is a preferred region for ultrasound based styling (heating+cavitation).

Region 2 is a preferred region for ultrasound based drying (nebulization).

Region 3 is a preferred region for ultrasound based styling & drying.

Region 4 is a preferred region for ultrasound based styling (heating).

For cavitation to take place at least a thin film of liquid has to be present on the hairs. During the drying phase cavitation can play a role to enhance the drying process. Styling should preferably only take place once the hair has fully dried to prevent cavitation from happening. Especially at higher power cavitation can damage the hair structure. In this case two non-overlapping frequencies are preferred for several reasons:

We favor styling through ultrasound heating and/or non-thermal without cavitation. (Region 4). Cavitation may decrease the power needed, but it also brings increased risk of damaging the hairs (Region 1). We do not exclude to use cavitation for styling, but preferably it is not used.

Drying through nebulization with high power using cavitation can be damaging to the hairs and therefore a more gentle form of nebulization is preferred (Region 2). We do not exclude to use cavitation to increase nebulization speed, but preferably it is not used.

A combined ultrasound styling & drying effect requires a very narrow frequency range and a setup with little losses (Region 3). The threshold for styling through ultrasound heating will lie somewhere between the threshold as predicted by 100% absorption of ultrasound power in hairs (Curve A) and less efficient absorption of ultrasound power in hairs as found in experiments (Curve B), thus significantly shrinking the preferred region for ultrasound based styling & drying (Region 3). Variation in moisture content, relative humidity, hair density, hair diameter, volume etc. will all influence the preferred region for ultrasound based styling and drying, making it very hard to predict the right settings let alone to predetermine said parameters to fall in a viable frequency range for styling and drying. Therefore, in practice the preferred regions for styling (Region 2) or drying (Region 4) are better defined and more robust than the preferred region for styling and drying (Region 3).

FIG. 4 shows a second embodiment of an ultrasound hair care device for drying and styling hair in accordance with the present invention. The main features of the ultrasound hair drying system of FIG. 4 include an ultrasound generator 100, an ultrasound amplifier 101, three ultrasound transducers 102A, 102B, 102C (one for styling, one for drying, one for moisture sensing), a droplet handler 105, water film and droplets 103, 103A, a control system 106, a user interface 107, and a thermal detector 108 to prevent overheating. The ultrasound generator 100 generates fixed or variable low-voltage ultrasound pulses, with frequency, voltage and pulse duration controlled by the control system 106 depending on treatment settings selected through the user interface 107 and the moisture content of the hairs detected by the ultrasound receiver 102C. This will enable atomization of liquid (103A, 103B) from the hair surface 104. The resulting droplets will be removed or extracted by the droplet handler 105, which could be a simple air blower/extractor or something more complex.

The hair care device can then be made to be safe for use if it is carefully designed such that:

During operation, the transducer does not touch the skin/scalp;

During operation, there is a substantial distance between the transducer and skin/scalp, wherein within the distance a material with low acoustic impedance e.g. air, is present to allow reflection of any leaking ultrasound wave in the interface to the skin due to acoustic impedance mismatch, limiting the ultrasound intensity of more than 3 W/cm² to reach the skin, and;

During non-operation, the transducer does not emit ultrasound.

Piezoelectric crystals (PMUT or standard) are used to produce ultrasound (>20 kHz). Non-piezoelectric techniques like Capacitance Micro-machined Ultrasonic Transducers (CMUT) can be used for higher frequencies (typically up to ˜100 MHz) and can be used with this invention. These techniques use relatively small transducers and are cheaper, thereby making it attractive for both home use and semi-professional hair care applications.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. If CMUT transducers are used, a single ultrasound transducer may be used for both ultrasound frequencies. It is possible to have a hard switch between the different ultrasound frequencies in that below a certain moisture level the first frequency is produced while above that moisture level the second frequency is produced. It is alternatively possible to have a soft switch allowing for a gradual reduction of the intensity of the ultrasound produced at the first frequency, and a gradual increase of the intensity of the ultrasound produced at the second frequency, as a result of a decreasing moisture level of the hair. In such a soft switching embodiment, a look-up table is preferably used in the control unit for determining the intensities of the ultrasound produced at the first and second frequencies in dependence of the moisture level.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word “comprising” does not exclude the presence of elements or steps other than those listed in a claim. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and/or by means of a suitably programmed processor. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. 

1. An ultrasound hair care device for drying and styling hair, the ultrasound hair care device comprising: an ultrasound unit for applying ultrasound to the hair; a hair moisture measurement unit for measuring a moisture level of the hair; and a control unit for controlling the ultrasound unit based on the moisture level, wherein, in dependence on the moisture level, ultrasound is applied to the hair at a first frequency not exceeding 1 MHz for drying the hair, and/or at a second frequency of at least 1 MHz for styling the hair.
 2. An ultrasound hair care device as claimed in claim 1, wherein the first frequency does not exceed 0.5 MHz, and preferably does not exceed 0.4 MHz.
 3. An ultrasound hair care device as claimed in claim 1, wherein the second frequency is at least 5 MHz, and preferably between 6.4 MHz and 500 MHz.
 4. An ultrasound hair care device as claimed in claim 1, wherein an ultrasound intensity is at least 1 W/cm².
 5. An ultrasound hair care device as claimed in claim 1, wherein an ultrasound intensity does not exceed 10 W/cm².
 6. The hair care device as claimed in claim 1, wherein the control unit comprises a look-up-table for switching the ultrasound unit to operate at the first frequency and/or at the second frequency in dependence on the moisture level.
 7. A hair care method of drying and styling hair, the hair care method comprising: measuring a hair moisture level; and applying, in dependence of the hair moisture level, ultrasound to the hair at a first frequency not exceeding 1 MHz for drying the hair and/or at a second frequency of at least 1 MHz for styling the hair.
 8. A hair styling method as claimed in claim 7, wherein ultrasound is applied during a period not exceeding 2 minutes, and preferably not exceeding 1 minute. 